The increasing crowding of the electromagnetic spectrum as well as increased power demands of mobile devices both spur interest in wireless energy harvesting.
Typical energy harvesting devices are comprised of an antenna which induces AC current from gathered ambient EM radiation, and an AC-DC converter which converts the AC current to usable DC current. Simple energy harvesting devices have a simple rectifier and an antenna, when combined the devices are called, “rectennas” (rectifier-antenna).
For the purpose of energy harvesting many antenna designs were used and known including: dipole antennas, loop antennas, patch antennas, spiral antennas, slot antennas, etc.
For the purpose of EM energy harvesting devices, antenna designs are created in such a manner as to utilize ambient EM radiation in order to maximize the AC voltage directed to the AC-DC converter. In order to achieve an optimal antenna design for this purpose, designs are created with the following factors in mind: Omni-directionality, compact dimensions, wide bandwidth reception, low resonance frequency point, high efficiency, etc.
There are many difficulties in designing an optimal antenna that maximizes on all of the above factors, mainly due to the fact that often by increasing one factor, may result in decreasing other factors. For example:
In traditional antenna designs, a compact design will often result in low bandwidth (due to short electrical length) impairing the antenna's ability to receive energy from various EM sources that emit varied frequency signals. On the other hand, increasing dimensions to achieve wider bandwidth will result in an antenna that has no utility to many consumers that require a compact EM energy harvesting device to charge mobile devices such as phones, tablets, smart watches, cameras, etc.
Furthermore, using traditional antenna designs, a smaller antenna will become resonant while receiving much higher frequency waves, while ignoring all together lower frequency waves.
Thus, in order to maximize output voltage, the chosen antenna design must maximize frequency bandwidth reception. It is apparent to a person skilled in the art that while there is little difficulty in designing an antenna that collects only SHF radio waves (3-30 GHz), there is a difficulty in designing an antenna that has such high bandwidth that it also may collect waves in the SLF part of the spectrum (30-300 Hz), as well as other usefully energetic parts of the EM spectrum, for example: HF (3-30 MHz), VHF (30-300 MHz), UHF (300-3000 MHz), etc.
For the purpose of collecting HF waves and lower frequency, it is not advisable to use a typical 15 meter long dipole antenna that is required to effectively enable 10 MHz frequency wave exploitation. For this purpose, there is a need for a compact design that is much smaller and compact in order to enable utility in mobile electronics applications.
In addition, such an optimal antenna design must also incorporate superior reception capabilities in exchange for redundant broadcasting capabilities and also incorporating omni-directionality to receive signals from EM sources located in all directions in relation to the harvesting device. A traditional design that increases on such factors is the loop design. Unfortunately, the loop design requires increasing dimensions for lower frequency reception and wider bandwidth.
In addition, an optimal antenna design must become resonant at a lower frequency point in order to enjoy resonance from the collection of common frequency waves. Thus, unlike a simple loop antenna that in order to resonate at a 15 MHz frequency must have a 20 meter perimeter, which is too large for the purpose of mobile applications.
As is well known to one with ordinary skill in the art, an EM transmission consists of the near-field which generally exists within one wavelength of the EM source's frequency and the far-field at distances greater than two wavelengths. Between the near and far-fields (between one and two wavelengths distance from the EM transmission) is found a transition zone, where far-field effects generally dominate. In the far-field, electric and magnetic fields are associated with each other and the ratio of the field intensities are known as the wave impedance, while in the near-field, the electric and magnetic fields can both exist independently and one field may dominate the other.
As is also well known to a person with ordinary skill in the art, a receiving antenna which is “electrically shorter” than ½ wavelength of the EM transmission may be caused to efficiently (by up to orders of magnitude) receive the EM transmission energy and effectively transduce it to AC by two means: inductively (by causing an induced current in an appropriate conductor) for the near-field, and resonantly (by causing the antenna to resonate at the frequency of the EM transmission) for both the near and far-fields.
Furthermore, through techniques which are familiar to one with ordinary skill in the art, such as controlled feedback oscillator loop coupling, with an LC circuit (tuned) it is possible to cause ‘regeneration’ thereby increasing the amplification factor of up to 15,000 or more.
Additionally, a technique familiar to one with ordinary skill in the art, using a type of antenna utilizing a core made of a material appropriate to frequency or frequencies an antenna is exposed to and desired to receive will extremely enhance the bandwidths of such an antenna, for example the so-called “Ferrite Rod Antenna”, used almost always in portable receivers for receiving broadcasts in long, medium and sometimes short wave bands. However, these antennas suffer certain drawbacks, including but not limited to: weight despite compactness, certain losses due to core material losses at certain frequencies, null area(s) due to shape, etc.
In the exemplary embodiments disclosed herein, a novel and non-obvious solution has been found to the aforementioned shortcomings, which gains the benefits of the aforementioned “Ferrite Rod” type antennae as well as other types of “cored” antennae, without the drawbacks, and has been found to additionally increase the Q of said exemplary embodiments disclosed herein significantly, by means of inserting ferromagnetic or ferroelectric polymer layer(s) (or, alternatively, a combination of these materials) between the conductive layers of the exemplary embodiments disclosed herein, depending upon the particular application attributes, for the purpose of effecting enhancement of magnetic or electric field (or any particular combination thereof) reception/harvesting and transduction efficiency.
Combining the aforementioned and following methods with an apparatus as described herein, is not obvious to one skilled in the art and will result in a novel and inventive compact device capable of aggregating wide bandwidths highly efficiently.
Furthermore, there is a need in creating an efficient design that allows exploiting both opposite phases of a wave in the same frequency without suffering destructive interference. Said optimal design will then achieve an output power that is double than the expected power of a regular antenna without the need of using multiple antennas per a harvesting device.
Thus exists a long felt need to achieve a new antenna design for energy harvesting purposes with the following features:                a. Wide bandwidth allowing efficient reception of SLF to SHF EM waves.        b. Superior reception capabilities.        c. Minimal or no antenna radiation/transmission.        d. Low frequency and multi-frequency resonance points.        e. Compact dimensions.        f. Efficient design that allows exploiting both opposite phases of a wave in the same frequency.        g. Optimised design for output AC phase angles closest to zero degrees, in order to maximize real/active power (“P”), as in the equation for AC circuits: P=VRMS×IRMS×cos θ.        h. Ability of antenna to operate both resonantly and inductively, in order to receive both ambient EM transmissions and from near-field induction (such as NFC, for example).        i. Capability to further enhance Q and efficiency as well as exploit more fully electric and magnetic field reception/harvesting (including static electrostatic and magneto-static fields).        